TDD

Question 1

Why use TDD?

Answer 1

• Improved test coverage leads to 40% - 80% fewer bugs in production (comparable to alternatives like design review, code review, and lint tools; much better than static types)
• Eradicates fear of change => Smooth CI/CD
• Fast developer feedback loop

Question 2

What is the TDD process?

Answer 2

1. Red - Before writing implementation code, write a test and watch it fail
2. Green - Write the smallest amount of code required to make the test pass, and watch the test pass
3. Refactor - Refactor if needed; the test will help you refactor with confidence

Question 3

Why write tests first?

Answer 3

• Encourages loose coupling – more modular architecture
• Think about APIs before implementation, leading to better developer experience
• Form a hypothesis first, removing hindsight bias

Question 4

Explain RITE way

Answer 4

R - Readable (did I answer the 5 questions?)

I - Isolated/Integrated
Isolated code under test, isolated tests from each other. Tests should be able to run in any order, and in parallel.
Integrated - Unit of code under test needs to be tested in integration with other units of code (and in the context of the app)

T - Thorough - test likely edge cases (zero, one, range boundaries, interfaces)

E - Explicit - Everything you need to know to understand a test is defined inside the test.

Question 5

What are the 5 questions every unit test must answer?

Answer 5

1. What component?
2. What is the behavior under test? (human-readable prose description)
3. Actual result?
4. Expected result?
5. How do you reproduce if the test fails? (Sanity check - did I answer the other questions well?)

Question 6

What is the difference between unit tests and integration tests?

Answer 6

Unit - Tiny, fast, cheap (good foundation), but if you’re not testing integrations, you’re not testing integrations.

Integration - Big, slow, clunky, expensive